The present invention relates to the control of fungal and/or bacterial infections of plants by actinomycetes that are antagonistic to, or produce materials antagonistic to undesired fungi or bacteria.
Fungal or bacterial phytopathogens are a cause of substantial economic losses in the agriculture, forestry, and horticulture industries. It is estimated that approximately four billion dollars are lost annually to disease. Many types of plant pathogens have been described including those that cause disease symptoms called damping-off, root-rot, wilt, blights, or stem and leaf rots. Such diseases can kill emerging seedlings, reduce plant robustness, and adversely affect crop yields.
Traditionally, breeding for resistant plants, sterilizing the soil either physically (e.g. steam) or chemically (e.g. methyl bromide fumigation) or chemical fungicide application has been attempted for control of phytopathogens. However, each of these methods has serious drawbacks. Completely resistant cultivars have not been developed. Soil sterilization is expensive and removes beneficial microorganisms that naturally compete against phytopathogens. Methyl bromide fumigation is being regulated out of existence. The use of chemical fungicides or bacteriostats to control phytopathogens has come under closer scrutiny due to their expense, lack of efficacy, limited effective duration, emergence of resistant pathogens, and regulation. Additionally, the use of chemicals for pathogen eradication is not desirable due to their toxicity to humans and the environment.
Biological control of plant pathogens is defined as the use of one or more biological processes to lower inoculum density of the pathogen or reduce its disease producing activities. The mechanisms underlying these processes include competitive exclusion of the pathogens(s), antibiosis, mycoparasitism, or induced resistance of the plant.
Microbial control as a means for protecting plants from pathogens provides an advantage over traditional control measures in that the biocontrol microorganisms grow and proliferate under conditions favorable for plant growth. Thus the effective concentration of the control agent can increase during the growing season, rather than decrease, as occurs with chemical control measures. The environment is not unduly degraded, and may in fact be upgraded, in that these microorganisms are a natural constituent of the environment and supply essential nutrient cycling functions. Due to the multiple mechanistic nature of biological control, the possibility of pathogens acquiring resistance to these controls are either eliminated (competitive exclusion, mycoparasitism) or drastically reduced (antibiosis). Furthermore, it is an established fact that plants may acquire microbial-mediated resistance factors towards the pathogen (induced resistance), thus providing a secondary defense mechanism.
Members of the Actinomycetales family are especially useful as biological agents for reducing phytopathogen infection in that they produce over 60% of the approximately 5,000 known antibiotics, some strains synthesizing 30 or more including many with fungicidal activity. They produce an enormous diversity of hydrolytic enzymes including enzymes that degrade fungal cell wall components, such as chitinases, cellulases, and glucanases. They are heterotrophically diverse, as they are evolutionarily adapted for growth in the soil or in close proximity to plant roots utilizing a wide range of carbon sources. They produce spores under environmental deleterious conditions. They grow vegetatively as mycelia, thus allowing root colonization and translocation of nutrients over relatively large distances.
The object of the present invention is to provide a new biological control means of reducing fungal or bacterial pathogen infection of plants.